Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$156.89	7.313%	$168.3634	$168.36	$168.35	$168.40
Purchase #2	$98.34	6.429%	$104.6623	$104.66	$104.65	$104.70
Purchase #3	$108.37	3.356%	$112.0069	$112.01	$112.00	$112.00
Purchase #4	$70.89	11.160%	$78.8013	$78.80	$78.80	$78.80
Purchase #5	$180.42	4.603%	$188.7247	$188.72	$188.70	$188.70
Purchase #6	$227.38	3.106%	$234.4424	$234.44	$234.45	$234.40
Purchase #7	$8.25	4.116%	$8.5896	$8.59	$8.60	$8.60
7 purchase totals =	$850.54		$895.5906	$895.58	$895.55	$895.60